Re: [PULL 3/9] tests/migration: Reduce autoconverge initial bandwidth

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Jun 09, 2020 at 06:00:17PM +0100, Dr. David Alan Gilbert wrote:
> * Michael S. Tsirkin (mst@redhat.com) wrote:
> > On Wed, Mar 25, 2020 at 01:16:26PM +0000, Dr. David Alan Gilbert (git) wrote:
> > > From: Philippe Mathieu-Daudé <philmd@redhat.com>
> > > 
> > > When using max-bandwidth=~100Mb/s, this test fails on Travis-CI
> > > s390x when configured with --disable-tcg:
> > > 
> > >   $ make check-qtest
> > >     TEST    check-qtest-s390x: tests/qtest/boot-serial-test
> > >   qemu-system-s390x: -accel tcg: invalid accelerator tcg
> > >   qemu-system-s390x: falling back to KVM
> > >     TEST    check-qtest-s390x: tests/qtest/pxe-test
> > >     TEST    check-qtest-s390x: tests/qtest/test-netfilter
> > >     TEST    check-qtest-s390x: tests/qtest/test-filter-mirror
> > >     TEST    check-qtest-s390x: tests/qtest/test-filter-redirector
> > >     TEST    check-qtest-s390x: tests/qtest/drive_del-test
> > >     TEST    check-qtest-s390x: tests/qtest/device-plug-test
> > >     TEST    check-qtest-s390x: tests/qtest/virtio-ccw-test
> > >     TEST    check-qtest-s390x: tests/qtest/cpu-plug-test
> > >     TEST    check-qtest-s390x: tests/qtest/migration-test
> > >   **
> > >   ERROR:tests/qtest/migration-test.c:1229:test_migrate_auto_converge: 'got_stop' should be FALSE
> > >   ERROR - Bail out! ERROR:tests/qtest/migration-test.c:1229:test_migrate_auto_converge: 'got_stop' should be FALSE
> > >   make: *** [tests/Makefile.include:633: check-qtest-s390x] Error 1
> > > 
> > > Per David Gilbert, "it could just be the writing is slow on s390
> > > and the migration thread fast; in which case the autocomplete
> > > wouldn't be needed. Perhaps we just need to reduce the bandwidth
> > > limit."
> > > 
> > > Tuning the threshold by reducing the initial bandwidth makes the
> > > autoconverge test pass.
> > > 
> > > Suggested-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > > Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> > > Message-Id: <20200323184015.11565-1-philmd@redhat.com>
> > > Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > > Tested-by: Alex Bennée <alex.bennee@linaro.org>
> > > Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > 
> > 
> > This slows make check down significantly for me, it stays
> > at the migration test for minutes.
> 
> Is this on the s390x version or all of them?

x86 slows down for me.

> > I'm carrying a revert at top of my tree for now but I'd rather
> > not need that.
> > 
> > 
> > This seems like a fragile way to test things anyway.
> > What happens if someone slows writing even more
> > e.g. because it's running in a container or a VM?
> > 
> > How about detecting that migration finished too early
> > and slowing it down until autocomplete triggers?
> 
> THe problem is you can't rely on any form of consistency in a heavily
> contended container, so the fact that it took n-seconds to migrate at
> this attempt means very little about what the next attempt will take.
> 
> Dave

What I'm saying is try migrating quickly. If it's too quick
try again ...

> > 
> > 
> > > ---
> > >  tests/qtest/migration-test.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/tests/qtest/migration-test.c b/tests/qtest/migration-test.c
> > > index 3d6cc83b88..2568c9529c 100644
> > > --- a/tests/qtest/migration-test.c
> > > +++ b/tests/qtest/migration-test.c
> > > @@ -1211,7 +1211,7 @@ static void test_migrate_auto_converge(void)
> > >       * without throttling.
> > >       */
> > >      migrate_set_parameter_int(from, "downtime-limit", 1);
> > > -    migrate_set_parameter_int(from, "max-bandwidth", 100000000); /* ~100Mb/s */
> > > +    migrate_set_parameter_int(from, "max-bandwidth", 1000000); /* ~1Mb/s */
> > >  
> > >      /* To check remaining size after precopy */
> > >      migrate_set_capability(from, "pause-before-switchover", true);
> > > -- 
> > > 2.25.1
> > > 
> > > 
> > 
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK